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\section*{Option 1: Intelligent life is rare}  On Earth it took more than 3 billion years for life to evolve from single-celled bacteria to Homo Sapiens. This is a long time compared to the emergence of "simple" life-forms, an argument often  used to conclude that $f_i \ll 1$. Scientists P. Ward and D. Brownlee in their book \href{http://bit.ly/1GGQt5B}{"Rare Earth"} claim that "Intelligent life on Earth relied on so many unlikely accidents that we are probably alone in the Universe". Is there anybody out there? --\textit{ silence} --